1. Field of the Invention
This invention relates generally to a spray dampening system for use with webs of varying sizes.
2. Description of Related Art
It is well known that the printing plate of a printing press is chemically treated so that only the printing area is receptive to ink. The non-printing area, on the other hand, is hydrophilic and receptive only to a dampening fluid, such as water. When the dampening fluid is applied to the plate, the water beads up on the printing area and is retained by the non-printing area. Consequently, the dampening water retained by the non-printing area creates a film barrier between the inking rollers and the non-printing area while the printing area, with no film of dampening water, accepts the ink. The ink is then transferred from the printing area of the plate and eventually to the paper web. The dampening water also serves to keep the rollers of the press lubricated. The dampening water can be applied by a variety of dampening water supply systems. One such system, spray bar dampening systems, is well known in the art.
In general, in a spray bar dampening system, the dampening fluid is sprayed onto a dampening roller by means of a series of nozzles. The dampening roller then transfers the dampening fluid to the other rollers of the press that are in serial contact with it. Proper and efficient operation of the press requires that the correct amount of dampening fluid be used and that the dampening fluid be applied in a uniform distribution and acceptable pattern. Applying the correct amount of dampening fluid in a uniform distribution and acceptable pattern is particularly difficult when using webs of different widths on a given press.
With regard to the pattern of dampening fluid spray, it is desirable to have the page breaks of the print aligned with the nozzle overlaps. First, because no printing generally occurs at the page breaks, little dampening water is needed in these areas. Second, overlaps in nozzle spray can have the effect of providing inconsistent ink densities on the printing area of the web. Therefore, in order to minimize such inconsistencies, it is desirable to ensure that nozzle spray overlaps occur at page breaks.
Furthermore, when utilizing a conventional spray bar system with a partial web having a relatively narrow width, the extreme outside edges of the spray pattern have no web to remove the dampening fluid. Thus, although the ends of the rollers require a small amount of dampening fluid to lubricate them, the non-web area of the rollers easily become flooded. In order to avoid flooding of the non-web area, attempts have been made to reduce the amount of water supplied by the outer nozzles. Alternatively, the outer nozzles would be turned completely off. Such attempts have been unsuccessful. Because the outer nozzles also supply dampening fluid to a portion of the printing area, there is a corresponding reduction in dampening water supplied to the printing area of the web. This reduction is unacceptable for reliable, quality printing. For example, it may be desirable to operate a newspaper printing press with a double wide web having a width of 55 inches as well as a partial web having a smaller width of 51 inches. Conventional spray bar systems for the double wide web are typically designed using eight nozzles for the four pages of the web. The page breaks coincide with the nozzle overlaps between the second and third nozzle, the fourth and fifth nozzle, and the sixth and seventh nozzle. These page breaks would occur at approximately 13.75 inches, 27.5 inches, and 41.25 inches from one end of the spray bar. Using a newspaper press having a conventional spray bar system to print a partial web of 51 inches, however, causes the page breaks and the nozzle overlaps to become misaligned because each page is 1 inch narrower. Additionally, each edge of the web would have moved towards the center of the press by two inches. These same problems exist when attempting to operate other presses, such as single wide presses and directory presses, with multiple webs of different widths.
Attempts have been made to allow a single spray bar system to be used with webs of different widths. For example, U.S. Pat. No. 5,025,722 to Switall et al. is directed to the adjustment of the positioning of the nozzles, and as such, the spray pattern of a spray bar system. The spray nozzles are laterally movable both towards and away from each other and at the same time, axially movable towards and away from the surface on which the dampening fluid is being applied. In general, the nozzles are mounted on nozzle carriages, each carriage having a follower. The nozzle carriages are axially slidable along a vertical guide track for movement towards and away from the dampening surface. Each follower is positioned in a guideway which restricts each follower's movement to a predetermined path in which they are properly spaced, both laterally and axially. Movement of the followers within the guideways is effected by connecting the followers cam members. The cam members, each having a rack formation, meshingly engage pinion members for allowing the cam members to move relative to each other. With multiple moving parts, however, the disclosed apparatus is complex in design and operation. Thus, manufacture and maintenance of the spray bar can be costly and time-consuming.
3. Objects of the Invention
It is thus an object of the present invention to provide a spray bar for use with webs of different widths.
It is another object of the present invention to provide a spray bar for use with webs of different widths that is simple in operation.
It is another object of the present invention to provide a spray bar for use with the webs of different widths that is easily manufactured.
It is still another object of the present invention to provide a spray bar for use with webs of different widths that is capable of positioning the of nozzles in either of two predetermined configurations.
It is yet another object of the present invention to provide a spray bar for use with webs of different widths that is capable of positioning the nozzle spray overlap in either of two pre-determined configurations.